﻿338 
  CONTRIBUTIONS 
  TO 
  TIIE 
  GEOLOGY 
  OP 
  

  

  Point 
  is 
  about 
  three 
  feet, 
  at 
  Evergreen 
  upwards 
  of 
  ten, 
  measured 
  to 
  the 
  

   upper 
  edge 
  of 
  the 
  stratum. 
  It 
  continues 
  downwards 
  to 
  a 
  depth 
  of 
  six 
  or 
  

   eight 
  feet, 
  and 
  terminates 
  in 
  an 
  argillaceous 
  clay 
  of 
  a 
  bluish-gray 
  co- 
  

   lour. 
  This 
  dark 
  stratum 
  consists 
  largely 
  of 
  particles 
  of 
  green 
  sand, 
  or 
  

   silicate 
  of 
  iron 
  and 
  potash. 
  It 
  contains 
  a 
  great 
  number 
  of 
  Eocene 
  fos- 
  

   sils, 
  among 
  which 
  are 
  Cardita 
  planicosta, 
  Fusus 
  longaevis, 
  &c. 
  &c. 
  al- 
  

   ready 
  known 
  as 
  existing 
  either 
  in 
  the 
  Eocene 
  of 
  Paris 
  or 
  Alabama, 
  or 
  

   in 
  both. 
  But 
  besides 
  these 
  it 
  also 
  contains 
  a 
  variety 
  of 
  beautiful 
  and 
  

   new 
  species, 
  some 
  of 
  which 
  will 
  be 
  described 
  in 
  the 
  present 
  paper. 
  

   These 
  shells 
  are, 
  at 
  some 
  points, 
  almost 
  entirely 
  dissolved, 
  and 
  very 
  

   perfect 
  casts 
  alone 
  can 
  be 
  procured 
  ; 
  but 
  at 
  other 
  points, 
  though 
  in 
  a 
  

   soft 
  condition, 
  they 
  can, 
  by 
  using 
  great 
  care, 
  be 
  obtained 
  in 
  an 
  entire 
  

   state. 
  

  

  38. 
  Above 
  this 
  stratum 
  is 
  a 
  layer 
  of 
  what 
  Mr 
  Edmund 
  Ruffin, 
  the 
  

   able 
  editor 
  of 
  the 
  Farmer's 
  Register 
  of 
  Virginia, 
  calls 
  gypseous 
  earth. 
  

   This 
  stratum 
  appears 
  once 
  to 
  have 
  abounded 
  in 
  fossils, 
  but 
  at 
  present 
  

   only 
  casts, 
  and 
  those 
  in 
  a 
  very 
  soft 
  condition, 
  can 
  be 
  found. 
  They 
  are, 
  

   however, 
  identical 
  with 
  the 
  fossils 
  of 
  the 
  lower 
  stratum. 
  The 
  earth 
  

   of 
  this 
  layer, 
  besides 
  a 
  considerable 
  proportion 
  of 
  green 
  sand, 
  contains 
  

   a 
  large 
  amount 
  of 
  sulphate 
  of 
  lime, 
  disseminated 
  in 
  minute 
  grains, 
  and 
  

   grouped 
  in 
  large 
  and 
  massive 
  crystals. 
  Immediately 
  above 
  occurs 
  a 
  

   thin 
  stratum 
  of 
  white 
  clay, 
  at 
  the 
  junction 
  of 
  which 
  with 
  the 
  former 
  

   layer 
  the 
  crystallized 
  gypsum 
  is 
  found 
  in 
  great 
  abundance, 
  and 
  almost 
  

   perfectly 
  pure. 
  Above 
  the 
  clay 
  is 
  a 
  stratum 
  of 
  shells 
  in 
  a 
  very 
  disin- 
  

   tegrated 
  condition, 
  but 
  consisting 
  of 
  Ostrea 
  sellaeformis 
  and 
  other 
  Eocene 
  

   fossils, 
  and 
  immediately 
  above 
  is 
  a 
  stratum 
  of 
  the 
  shells 
  of 
  our 
  middle 
  

   Tertiary. 
  A 
  few 
  scattered 
  pebbles 
  of 
  a 
  brown 
  hue, 
  hardly 
  numerous 
  

   enough 
  to 
  form 
  a 
  stratum, 
  separate 
  these 
  two 
  very 
  distinct 
  formations. 
  

   In 
  this 
  uppermost 
  layer 
  are 
  found 
  the 
  common 
  Pecten 
  and 
  Pectunculus 
  

   of 
  our 
  middle 
  Tertiary.* 
  The 
  whole 
  thickness 
  of 
  the 
  Eocene 
  deposit 
  

  

  Among 
  the 
  interesting 
  fossils 
  of 
  the 
  middle 
  Tertiary 
  above, 
  is 
  an 
  enormous 
  specimen 
  of 
  

   Astrea, 
  which 
  is 
  worthy 
  of 
  being 
  described. 
  This 
  mass 
  was 
  some 
  years 
  ago 
  disengaged 
  from 
  

   the 
  upper 
  part 
  of 
  the 
  cliff 
  at 
  Torbay, 
  and 
  is 
  now 
  lying 
  on 
  the 
  shore, 
  firmly 
  fixed 
  in 
  the 
  sand 
  

   and 
  clay. 
  Though 
  it 
  has 
  been 
  much 
  reduced 
  in 
  size 
  since 
  its 
  fall, 
  it 
  is 
  still 
  of 
  immense 
  mag- 
  

   nitude. 
  Its 
  form 
  is 
  of 
  course 
  very 
  irregular, 
  but 
  its 
  largest 
  diameter 
  may 
  be 
  estimated 
  at 
  four 
  

  

  